1. Field of the Invention
The present invention generally relates to spray-deposited production of a product on a moving substrate and, more particularly, is concerned with a vertical orientation of the substrate for minimizing recirculation of overspray.
2. Description of the Prior Art
A commercial process for production of spray-deposited, shaped preforms in a wide range of alloys has been developed by Osprey Metals Ltd. of West Glamorgan, United Kingdom. The Osprey process, as it is generally known, is disclosed in detail in U.K. Pat. Nos. 1,379,261 and 1,472,939 and U.S. Pat. Nos. 3,826,301 and 3,909,921 and in publications entitled "The Osprey Preform Process" by R. W. Evans et al, Powder Metallurgy, Vol. 28, No. 1 (1985), pages 13-20 and "The Osprey Process for the Production of Spray-Deposited Roll, Disc, Tube and Billet Preforms" by A. G. Leatham et al, Modern Developments in Powder Metallurgy, Vols. 15-17 (1985), pages 157-173.
The Osprey process is essentially a rapid solidification technique for the direct conversion of liquid metal into shaped preforms by means of an integrated gas-atomizing/spray-depositing operation. In the Osprey process, a controlled stream of molten metal is poured into a gas-atomizing device where it is impacted by high-velocity jets of gas, usually nitrogen or argon. The resulting spray of metal particles is directed onto a "collector" where the hot particles re-coalesce to form a highly dense preform. The collector is fixed to a mechanism which is programmed to perform a sequence of movements within the spray, so that the desired preform shape can be generated. The preform can then be further processed, normally by hot-working, to form a semi-finished or finished product.
The Osprey process has also been proposed for producing strip or plate or spray-coated strip or plate, as disclosed in European Pat. Appln. No. 225,080. For producing these products, a horizontal substrate or collector system, such as a flat substrate or an endless belt, is moved continuously through the spray to receive a deposit of uniform thickness across its width.
A potential problem associated with employment of the Osprey process for strip production using a horizontal substrate system is entrainment of overspray particles in the product. These solidified droplets and/or splats are undesirable since they can produce voids, oxide inclusions, etc., resulting in unacceptable product quality. Entrainment of overspray is a consequence of secondary gas flows in the spray chamber which can recirculate overspray particles upwardly back into the atomizer region.
Ideally, gas flow should allow overspray particles to fall directly to the bottom of the spray chamber where they cannot be recirculated. However, in strip production using the horizontal substrate system, gas flow is such that secondary vortices above the strip are difficult to avoid and so incorporation can readily occur.
Therefore, a need exists for an approach for reducing the overspray recirculation problem in order to improve the quality of strip product produced by the above-described Osprey spray-deposition process.